Radio receiver



July29, 1941. SWT 1 2,251,075

RADIO RECEIVER Filed July 11, 1939 3 Sheets-Sheet 1 July 29, 1941. G.SMITH 2,251,075

RADIO RECEIVER I Filed July 11, 1959 Sheets-Sheet 2 July 29, 1941. G,SWTH 2,251,075

RADIO RECEIVER Filed July 11, 1939 3 Sheets-Sheet 3 Patented July 29,194i UNITED STATES PATENT OFFICE RADIO RECEIVER Graydon Smith,Cambridge, Mass, assignor to National Company, Inc., Malden, Mass, acorporation of Massachusetts Application July 11, 1939, Serial No.283,854

1 other words, my invention results in a receiver 3 Claims.

This invention relates to radio receivers and in particular consists ina novel mechanism for changing the coils in a receiver in order to shiftfrom one frequency band to another.

Modern communication receivers are designed to be operated withinterchangeable sets of coils so that one receiver can cover a widerange of frequencies by being connected to different sets of coils forthe different frequency bands.

It is important that the leads connecting the tubes, coils, and tuningcondenser be as short and direct as possible and also of constantcharacteristics. At high frequencies the inductance of the leads Will beappreciable in comparison with the coil inductance, so that any changein the inductance of the leads due to a change in the position of theleads or switch parts will seriously affect the calibration of thereceiver. Furthermore, the distributed capacity of the leads is inparallel with the tuning condenser, so that it must be held to a lowvalue to avoid reducing the tuning range. In addition, the inductanceand capacitance contributed by the leads will not be as low in losses asthat provided by the coils and condensers, so that it is desirable toconcentrate all the inductance in the coils and all the capacitance inthe condensers, so far as possible, in order to achieve highselectivity.

The ordinary communication receiver is provided either withaccommodations for one set of plug-in coils, in which case there may beas many as 50 sets which may be employed in order to cover a wide rangeof frequencies, or with four or five sets of coils permanently builtinto the receiver with mechanism for switching from one set of coils toanother. In the first instance the receiver is flexible but inconvenientto operate, since one set of coils must be removed and another setinserted whenever the range of frequencies is to be changed. In thelatter instance the range can be changed easily, but the receiver islimited to the range of frequencies attainable by the sets of coilsbuilt into it.

The most important object of my invention is to provide a receiverequipped for holding a substantial number of easily removable sets ofcoils together with mechanism for switching from one set to another.With this novel combination, it is possible to insert in the receiver anumber of sets of coils which will cover all the frequency ranges usedfor a certain type of operation such as amateur bands, airlinecommunication bands, etc. However, the sets of coils can be easily andquickly replaced With a number of different sets of coils permittingoperation of another type. In

combining the advantages of the plug-in coil receiver and the receiveremploying a limited number of built-in sets of coils.

Another object of my invention is to provide adequate stage shielding.For this purpose I provide individual shields for each .0011 to preventfeed back and general instability between the various stages of thereceiver. Furthermore the shields are adequate to prevent disconnectedcoils from affecting the coils connected in the circuit, when thenatural frequency of a disconnected coil is approached.

One important feature of the invention resides in mechanism for changingthe coils, or switching to different bands, utilizing leads which arenot only short but are also of uniform length. Another feature of theinvention resides in coils so placed that the trimmer condensersassociated with them can be easily adjusted with a socket wrench whilethe coils are in operation.

An important advantage of my novel construction is that a number of setsof coils covering certain frequency ranges can be inserted in thereceiver and selectively connected in the circuit and yet be easilyreplaced with other sets of coils covering different frequency ranges.

These and other features of the invention will be more readilyunderstood and appreciated from the following detailed description of apreferred embodiment thereof, selected for purposes of illustration andshown in the accompanying drawings, in which:

Fig. 1 is a plan view of portions of a receiver including the coilholders, rotary switch member and circuit contacts,

Fig. 2 is an end view of the support for the sets of coils and showingdiagrammatically the location of the condensers and tubes,

Fig. 3 is a plan View of a .coil holder sectioned in part to show thedisposition of one of the coils,

Fig. 4 is a view in end elevation of the cam controlled switch member,

Fig. 5 is a view in perspective of a coil mounted in its shieldedholder,

Fig. 6 is a view in end elevation of one of the coil holders,

Figs. '7 and 8 are respectively plan and end elevation views of amodified mechanism, and

Fig. 9 is a view in end elevation of one of the coil holders used withthe modified mechanism.

Before proceeding to a description of the drawings, I wish it to beunderstood that the circuit used in the receiver forms no part of theinvention and that I contemplate the use of any cirinvention.

cuit or types of coils which may be conveniently employed by thoseskilled in the art.

The coil holding structure is designed to be permanently secured to thechassis of the receiver and, as shown in Figs. 1 and 2, includes asemi-cylindrical skeleton frame of cast aluminum or other suitablematerial indicated generally by the reference numeral If). The frame ifpresents a series of longitudinally disposed receptacles consisting of aplurality of transverse sections or pockets spaced and secured togetherby longitudinal struts l4, and each section comprises a semi-circularhub member it from which an apertured bearing l8 extends inwardly andfrom which radial spokes 26 extend outwardly, being joined at theirouter ends by the struts l4 and by lateral spaces l'l. Two of the spokes28 are vertical and are tapped in four places so that they may besecured to a partition it which is part of the chassis of a receiver.The bearing 28 is also tapped for a securing screw 22 which providesfurther anchorage for the frame it against the partition 2.

The frame it illustrated in Figs. 1 and 2 provides accommodations forfive sets of four coils each. The gangs of coils are assembled inholders each consisting of a base plate 25 to which are screwed fourshields 28 of aluminum, or other suitable material, forming wedge shapedcompartments open at their small ends. Two U-shaped sheet metal supports3% are screwed to the base plate 26 inside each compartment 23 and attheir upper ends support a block 32 of Bakelite or other insulatingmaterial apertured to receive four sets of contact members 3 1. Theblocks 32 just fill the open ends of the shields 2%.

Within the shields 28 and secured to the base plate are a series ofcoils, one of which is shown in Fig. 5, consisting of an insulated base36, a form 38 (upon which is wound a primary coil 9 and a secondary coil42), and a trimmer condenser i l to which the terminals of the secondarycoil 52 are connected. No further details of the coil construction arenecessary here inasmuch as the coils themselves form no part of the Itshould be stated, however, that the condenser dd may be adjusted byturning a nut 56 on the end of the rotor shaft of the condenser.

The nut 6-5 is located on the bottom of the base 36 and a hole isprovided in the base plate 26 so that the condenser G i may be adjustedfrom the outside of the shield 28 while the coil is in operation. Thecoil holders are held in the frame by thumb screws (-8 which secure thebase plate 23 to the lateral spacers l'l.

Secured to the partition 22 adjacent one end of the frame 29 is a gearbox 533 one side of which provides a bearing for a shaft 52 whichcarries a crank on its outer end, a universal joint 5% being employed toprovide for angular adjustment of the shaft A long bar 53 of Bakelite isarranged axially in the frame 29 and is connected at one end to theouter end of the crank 58. Secured at spaced intervals to the bar 55 arefour short U-shaped blocks 33 also of Bakelite and provided withapertures engaging pivot pins 62 passing through the bearings 58. Thebar 53 and the blocks 6% are apertured to receive contact members 64which extend outwardly on both sides of the bar 58 and the blocks 55. Onone side the ends of the contacts lie in the axis of rotation of thepins '52 and the shaft 52. The assembly of the blacks with the bar 5 3and the pins 32 and the contacts 64 may conveniently be termed a switchmember" 55. These ends are constantly connected to other contacts 6&3which are held in short blocks 83 of Bakelite which are secured to thepartition 12, the latter being provided with holes through which theother ends of the contacts Q5 pass.

It will be understood that when the shaft El] is rotated, the outer endsof the contacts 6 1 are turned from one line of coil contacts 34 toanother. The contacts S t may be termed circuit contacts since fixedleads connect them with the variable tuning condensers, tubes, and otherelements in the receiver. A condenser ill and a tube 72 are showndiagrammatically in Fig. 2 and their location illustrates how closelythey can be associated with the circuit contacts 84 and thus with thecoil contacts 3'2. Furthermore the length of the leads from the coils tothe circuit contacts 64 is uniform for all coils and for all sets ofcoils.

For controlling the movement of the shaft 52 a shaft 74 is provided. Atone end the shaft 14 carries a bevel gear l6 located in the gear box 59and in mesh with a larger bevel gear 78. The other end of the shaft 14extends through the front wall 82 of the receiver and carries a handle84.

Inside the wall 82 and secured on the shaft M is a hub 85 carrying adisk 88 divided at its edge into a plurality of segments providing aninsulating cam surface for a roller cam follower 95. The cam roller 95is journalled in one end of an arm 92 which is U-shaped in cross sectionand secured to a spring contact member 94. The other end of the arm 94is fast under a post 98, and another spring contact member 98 is alsosecured to the post 96 but insulated from the arm Q4 by an insulatingwasher iflfl. The spring contacts, which may be in the plate powercircuit, are closed except when the roller 9B is on the high portions ofthe cam track on the disk 88, at which times the contacts are forcedapart.

While not essential to the operation of the recelver, the use of the camoperated switch is a very desirable feature. For example it is poorpractice to open the grid circuit of an electronic tube while power isapplied to the plate as it is injurious to the cathode. In shifting fromone range to another the grid circuit of the first detector tube wouldbe open while the switch member was passing from one set of contacts tothe next, for example, and the switch described would automatically shutoff plate power during the transition. Furthermore, such a switch can bearranged to prevent undesirable noise in the loudspeaker or earphonesduring the switching operation, since it can operate at any convenientpoint in the power supply circuit, for example, in the lead from therectifier tube in which case the power supply filter would protect thereceiver circuits from surges when the switch was opened.

The roller 99 also acts as a detent to cause the shaft 52 to come torest when the contacts 64 are in precise connection with one set ofcontacts 36. When it is considered that some receivers can be tunedappreciably when the switch control knob is moved slightly, it will beobvious that the detent action of the roller is important in maintainingexact calibration. Furthermore the effect of any slight variation in thedetent action is minmized by the design of the switch contact arms whichkeeps the path of the current substantially unchanged.

Now that one embodiment of my invention has been described in detail itwill be apparent to those skilled in the art that, in one aspect, the

salient features of my invention consist in the frame I providing aseries of parallel sectioned pockets converging toward a commonlongitudinal axis at which is provided a rotatable contact memberarranged to be selectively engaged with contacts presented to the axisby the sets of coils held in the frame. This structure combines theflexibility of a receiver using plug-in coils with the coil shiftingease of a receiver equipped with a plurality of built-in coils.

The pockets, as will be understood, are defined by the radial spokes 20,the longitudinal struts I4, and the lateral spacers I1 and these pocketsconverge inwardly toward the longitudinal axis of symmetry of the frame.The coil holders and coils are complete, self-contained units arrangedto be conveniently slipped into or removed from the respective pockets.They are removably retained in place by the thumb screws 48 and can beeasily and quickly replaced by other sets of coils so that one receivercan cover an extremely wide range of frequencies.

It is also important to note that each coil in each set is carefully andcompletely shielded by the wedge shaped compartments 28 in which it isenclosed so that feed back and general instability due to couplingbetween the various stages of the receiver is effectually prevented.

A second embodiment of my invention is illustrated in Figs. 7-9. Thisdiffers from that already described principally in that the frame orcage containing the removable coil holders, instead of being stationaryand associated with a rotatable switch member, is itself rotatable andassociated with a stationary switch member located adjacent to itsperiphery instead of its axis.

The rotatable frame is supported in the chassis of the receiver upon ahorizontal shaft I82 extending between a pair of upstanding bracketmembers I03 and comprises skeleton end spiders I04 of substantiallyhexagonal shape spaced and connected by longitudinal rods I05. Threeintermediate spiders I06 divide the frame into four transverse sections,the construction of the frame being such as to provide six longitudinalpockets spaced radially about the shaft I02 as an axis. The shaft I82 isinterrupted to receive a universal joint 54 and carries at its outer enda bevel gear I9 meshing with a second bevel gear I6 and both enclosed inthe gear box already referred to in Fig. l. The mechanism for rotatingthe shaft I02 and the frame carried thereby is identical to that alreadydescribed in connection with the rotation of the switch shaft 52 exceptthat in this instance a cam disk 83 having six notches is provided inplace of the five-notched disk 88 shown in Fig. 4. Each one of thenotches in the disk 83 corresponds to one of the six longitudinalpockets in the rotatable frame and cooperates with a follower cam roll90 to register one of these pockets in horizontal position as shown inFig. 8 and to interrupt momentarily the power supply circuit during thetransition of the frame from one position to another.

The equipment for the mechanism shown in Figs. '7 and 8 includes anassortment of holders each comprising a base plate I01 carrying fourshields I08 forming wedge shaped compartments in each of which isenclosed a coil and trimming condenser of the same general constructionas illustrated in Fig. except that the terminals I09 project outwardlyfrom the base plate I01 instead of through the small end of the shield.Moreover the adjusting screw IIO for each condenser is arranged inregistration with an opening in the base plate I-DI so that it may beconveniently reached from outside the apparatus for adjusting thecondenser as may be required.

The switch member cooperating with the rotary frame comprises astationary bar III disposed longitudinally and located adjacent to oneside of the rotary frame at substantially the level of its shaft I Il2.-The switch bar II I is provided with a series of inwardly extendingcontact blades IIZ each of which is arranged to receive one of thecontacts I09 when the frame is rotated to make the connection. I Theswitch bar III is also provided with a series of corresponding outwardlyextending contact blades H3 for connection with the circuits of thereceiver.

As in the construction of Figs. 1 and 2 the coil holders are removablysecured in their respective pockets by screws I I4 threaded into theendmost spiders IE4. Accordingly by removing its four screws anyone ofthe holders may be slipped out of its pocket and replaced by anotherholder having a set of coils for a different band of frequencies. Thussix coil holders of four coils each are at all time available and anyselected holder may be brought into operative position by turning thehandle 84. On the other hand any one or all of the holders in the framemay be removed and others substituted according to the band of frequencyin which the receiver is to be used.

In both illustrated embodiments of the invention all the contacts areshort and of uniform length, as previously stated, and the trimmercondensers associated with the coils may conveniently be adjustedthrough the apertures in the base plates of the coil holders while thecoils are in operation. Finally, the provision of the cam-actuatedswitch results in a more efficient and generally satisfactory receiver.

Radio is a field which is famous for infinite variation, and myinvention is broader in scope than might be gathered from an inspectionof the drawings. The frame In of Fig. 1 as shown provides accommodationsfor five sets of four coils each (three R. F. coils and one oscillatorcoil) and the frame of Fig. '7 provides for six sets, but the number ofsets and the number of coils in each gang is a matter of choice and maybe varied according to the type of receiver with which they may be used.

Having thus described and illustrated my invention, what I claim as newand desire to secure by Letters Patent of the United States is:

l. A coil shifting mechanism for radio receivers, comprising asupporting frame providing parallel series of pockets, means for holdinga plurality of coils in said pockets with their inner ends converging toa common axis, contacts extending to the axis from the coils, circuitcontacts disposed adjacent said axis, and a long bar of insulatingmaterial provided with through and through contacts and rotatable insaid axis, one end of the contacts in the bar being constantly connectedto said circuit contact, and the other end of the contact in the barbeing arranged selectively to engage the contacts extending from thecoils.

2. A coil shifting mechanism comprising an arcuate frame providing aseries of pockets, means for holding a plurality of coils in saidpockets with their inner ends converging to a common axis, contactsextending toward the axis from the coils, circuit contacts disposed insaid axis, a long bar of insulating material disposed for rotation aboutsaid axis, a series of contacts disposed in said bar and protruding fromboth sides thereof, one end of each contact in the bar being constantlyengaged with one of said circuit contacts, and the other end of eachcontact in the bar being arranged selectively to engage the contactsextending from the coils.

3. A coil shifting mechanism for radio apparatus, comprising asupporting frame having members defining a series of parallelwedge-shaped pockets, a series of Wedge-shaped coil holders maintainedin said pockets and provided with contacts extending toward the axis ofthe frame, a series of circuit contacts secured to the frame adjacentthe axis thereof, a plurality of U-shaped blocks of insulating materialmounted for rotation about the axis of the frame, a long bar ofinsulating material secured to said U-shaped blocks, a crank secured tosaid long bar, and through and through contacts secured in and passingthrough said U-shaped blocks and said long bar, one end of each of thelatter contacts being constantly engaged with one of said circuitcontacts and the other end arranged selectively to engage the contactsextending from said coil holders.

GRAYDON SMITH.

